U.S. patent number 5,386,410 [Application Number 08/100,064] was granted by the patent office on 1995-01-31 for optical recording medium and recording and reproducing apparatus of the same.
This patent grant is currently assigned to Olympus Optical Co., Ltd.. Invention is credited to Yutaka Adachi, Tatsuo Nagasaki.
United States Patent |
5,386,410 |
Nagasaki , et al. |
January 31, 1995 |
Optical recording medium and recording and reproducing apparatus of
the same
Abstract
A recording and reproducing apparatus of an optical recording
medium has a plurality of light sources. A plurality of light beams
are radiated by a laser diode array to a track of the optical
recording medium, and each of the plurality of light beams
reflected by the track is detected by a photodiode and converted
into an electrical signal. The laser diode array is arranged such
that the beam spots of adjacent ones of the plurality of light
beams cross a track direction of the optical recording medium and a
track width direction perpendicular to the track direction. The
signal detected by the photodiode is converted into an electrical
signal and recorded in a frame memory as data corresponding to the
signal. The digital data stored in the frame memory is read out by
a two-dimensional decoder.
Inventors: |
Nagasaki; Tatsuo (Hachioji,
JP), Adachi; Yutaka (Hachioji, JP) |
Assignee: |
Olympus Optical Co., Ltd.
(Tokyo, JP)
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Family
ID: |
15565490 |
Appl.
No.: |
08/100,064 |
Filed: |
July 30, 1993 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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710675 |
Jun 5, 1991 |
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Foreign Application Priority Data
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Jun 12, 1990 [JP] |
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2-153575 |
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Current U.S.
Class: |
369/275.4;
369/111; G9B/20.009; G9B/7.039; G9B/7.068; G9B/7.103; G9B/7.134;
G9B/7.136 |
Current CPC
Class: |
G11B
7/0904 (20130101); G11B 7/127 (20130101); G11B
7/131 (20130101); G11B 7/14 (20130101); G11B
7/24085 (20130101); G11B 20/10 (20130101) |
Current International
Class: |
G11B
7/125 (20060101); G11B 20/10 (20060101); G11B
7/09 (20060101); G11B 7/13 (20060101); G11B
7/14 (20060101); G11B 7/013 (20060101); G11B
003/70 () |
Field of
Search: |
;369/44.11,44.23,44.34,44.37,44.41,44.42,109,110,111,112,124,48,122,275.3,275.4 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0245511 |
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Nov 1987 |
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EP |
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0350336 |
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Jan 1990 |
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EP |
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3545996 |
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Jul 1986 |
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DE |
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3724622 |
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Jan 1988 |
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DE |
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3741910 |
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Jun 1988 |
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DE |
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3837745 |
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May 1989 |
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DE |
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59-207433 |
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Nov 1984 |
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JP |
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63-58627 |
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Mar 1988 |
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JP |
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Primary Examiner: Psitos; Aristotells
Assistant Examiner: Hindi; Nabil
Attorney, Agent or Firm: Frishauf, Holtz, Goodman &
Woodward
Parent Case Text
This application is a continuation of application Ser. No.
07/710,675, filed Jun. 5, 1991 now abandoned.
Claims
What is claimed is:
1. An optical recording medium comprising:
a plurality of writing tracks;
a plurality of guide tracks respectively formed between two of said
plurality of writing tracks; and
a plurality of pits formed in each of said plurality of writing
tracks;
said plurality of writing tracks having data written therein, said
data being represented by distance between each of said plurality
of pits and one of said plurality of guide tracks adjacent to the
writing track in which said plurality of pits are formed.
2. The optical recording medium according to claim 1, wherein:
said data represented by said distance, written in said plurality
of writing tracks, is further represented by a distance between
adjacent pits when viewed in at least one of a track length
direction and a track width direction which is perpendicular to
said track length direction; and
said data represented by said distance, written in said plurality
of writing tracks, has a principal pit dimension in at least one of
said track length direction and said track width direction.
3. The optical recording medium according to claim 1, wherein said
data represented by said distance, written in said plurality of
writing tracks, is further represented by a pit depth.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical recording medium and a
recording and reproducing apparatus of the same and, more
particularly, to an optical recording medium on which data
multi-value recording is performed and a recording and reproducing
apparatus of the same.
2. Description of the Related Art
Recently, a recording and reproducing apparatus (e.g., an optical
disk apparatus) which uses an optical recording medium has begun to
be used as a large-capacity data recording apparatus. For example,
in this optical recording apparatus, a light beam emitted by a
laser optical source arranged above an optical disk as an optical
recording medium is focused as incident light by a polarization
beam splitter, an objective lens, and the like, and irradiates a
track of the optical disk. Light reflected by the optical disk is
directed to the polarization beam splitter to be separated from the
incident light, and supplied to a photodetector such as a
photodiode. An optical signal from the polarization beam splitter
is converted by the photodetector into an electrical signal and
amplified. Then, data written on the track of the optical disk is
read out as recorded data through a sample and hold circuit, a
digitizer, a decoder, and the like.
In such an optical disk apparatus, data to be recorded on a track
of an optical disk, i.e., recording pits are usually arranged along
the track direction in a one-dimensional manner. For this reason,
the recording pits are formed at desired intervals. However, this
imposes a limit in obtaining higher density data recording.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a
high-density optical data recording medium by using the pit size
realized by a conventional recording and reproducing apparatus, and
a recording and reproducing apparatus of the same.
According to an aspect of the present invention, there is provided
an optical recording medium comprising a plurality of tracks,
formed at a predetermined interval, for writing data therein, and a
plurality of guide tracks, formed between the plurality of tracks,
for writing data therein, wherein a pit as coded data is formed in
at least one of a track direction and a track width direction
perpendicular to the track direction by modulating at least one of
a pit length, an interpit distance, and a distance between the
guide track and the pit.
According to another aspect of the present invention, there is
provided a recording and reproducing apparatus of an optical
recording medium, comprising light beam radiating means having a
plurality of light sources for radiating a plurality of light beams
to the optical recording medium, photodetecting means for detecting
the plurality of light beams reflected by the optical recording
medium and converting the detected light beams into electrical
signals, memory means for recording data corresponding to the
signal detected by the photodetecting means, and decoding means for
reading out the signal stored in the memory means and decoding the
coded data, wherein the plurality of light sources of the light
beam radiating means are arranged such that beam spot positions of
adjacent ones of the plurality of light beams cross a track
direction of the optical recording medium and a track width
direction perpendicular to the track direction.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute
a part of the specification, illustrate presently preferred
embodiments of the invention, and together with the general
description given above and the detailed description of the
preferred embodiments given below, serve to explain the principles
of the invention.
FIG. 1A shows a moving spot reflection intensity of an optical
recording medium and a recording and reproducing apparatus of the
present invention;
FIG. 1B shows a relationship between the reflection intensity and a
band;
FIG. 2 schematically shows an optical system of a recording and
reproducing apparatus of an optical recording medium according to
the first embodiment of the present invention;
FIG. 3 is a block diagram of the main part of the recording and
reproducing apparatus of the optical recording medium;
FIG. 4 schematically shows a track of the optical recording
medium;
FIGS. 5A and 5B respectively show on- and off-track states;
FIG. 6 is a table showing the memory content of a frame memory of
FIG. 3;
FIG. 7 shows a state in which spots sequentially irradiate a track
of an optical recording medium;
FIG. 8 schematically shows an optical system of a recording and
reproducing apparatus of an optical recording medium according to
the second embodiment of the present invention;
FIG. 9 is a block diagram of the main part of the recording and
reproducing apparatus of the optical recording medium which adopts
the optical system of FIG. 8;
FIG. 10 shows an image-forming state on the surface of a photodiode
array of FIG. 8;
FIG. 11 schematically shows an optical system of a recording and
reproducing apparatus of an optical recording medium according to
the third embodiment of the present invention;
FIG. 12 is a block diagram of the main part of the recording and
reproducing apparatus of the optical recording medium which adopts
the optical system of FIG. 11;
FIG. 13 shows a scanning state on a track;
FIGS. 14A and 14B are waveform charts of a photodiode output
obtained by scanning in FIG. 13 and a pulse of an actuator for
moving a laser diode;
FIG. 15A shows the positional relationship between an optical
recording medium and a pickup of the fourth embodiment of the
present invention;
FIG. 15B shows the relationship between movements of a track of the
optical recording medium of FIG. 15A and spots;
FIG. 16 is a block diagram of the main part of a recording and
reproducing apparatus of the optical recording medium according to
the fourth embodiment of the present invention;
FIG. 17 schematically shows an optical system of a recording and
reproducing apparatus of an optical recording medium according to
the fifth embodiment of the present invention; and
FIG. 18 shows in-focus states of light beams of a laser diode array
in FIG. 17.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to the present invention, sampling is performed in a
track direction and a track width direction perpendicular to the
track direction in a two-dimensional manner at a sampling pitch
satisfying a sampling theorem, and the intensity of light reflected
by a sampling point is monitored. If a pit exists, the intensity of
the light reflected by the optical recording medium changes due to
phenomena such as diffraction. Hence, the reflected light intensity
reflects the presence/absence of a pit. The intensity of the light,
in each of the two-dimensional directions, reflected by the optical
recording medium and sampled in the two-dimensional directions at
the sampling pitch described above, is filtered through a low-pass
filter (LPF). As a result, the light intensity of each of the
two-dimensional directions is modulated to a distance, and
two-dimensional position data of multi-value recorded pits is
obtained.
Since this position data is obtained by a method satisfying the
sampling theorem, it precisely reproduces the two-dimensional
position of a pit. More specifically, in the present invention, a
pit position is detected without using a line sensor and the like
as a detecting system. Therefore, a detection resolution can be
increased and the number of multi-value recording steps can be
decreased independently of a resolution of a detector or the number
of detectors.
With a recording and reproducing apparatus of an optical recording
medium, assume that a plurality of light sources are sequentially
turned on one at a time as the light beam radiating means. In this
case, the arrangement pitch of the light sources in the track
direction of the optical recording medium is set to satisfy the
following relation: ##EQU1## where Px is the arrangement pitch of
the light beam sources in the track direction of the optical
recording medium, W is the minimum repetition cycle of the data
recording pits in the track direction, n is the number of the
plurality of light sources, and l is a natural number. The second
term .+-.W/2n of inequality (1) is to correct the distance of the
moving medium as the light sources are sequentially turned on. The
sign is determined by the moving direction of the medium. When the
plurality of light sources are turned on simultaneously, the above
relation may be:
When the arrangement pitch of the light beam sources in a direction
perpendicular to the track direction is Py, Py is set to satisfy
the following relation: ##EQU2## where a is the pitch width size in
a direction perpendicular to the track direction and T is the light
beam spot length (spot type) in the direction perpendicular to the
track direction. Since condition T>a is generally satisfied, the
plurality of light sources may be arranged such that spots are
formed on the medium to satisfy the following relation:
FIGS. 1A and 1B will be described. First, when a spot 10 moves in
the direction of an arrow H in FIG. 1A to cross a pit 12, the
reflected light intensity of the moving spot on a time base is
indicated as in FIG. 1A. Of the reflected light intensity, a
function having a widest band is a rectangle function having a
width of T+a. Its band is as shown in FIG. 1B, and a first
zero-crossing point is 1/(T+a). This band is the data recording
band in a direction perpendicular to the track direction. Thus, the
sampling pitch for correctly reproducing this band becomes as
indicated by inequality (3) from the sampling theorem.
In the recording and reproducing apparatus of the optical recording
medium, when a single light source is moved as the light beam
irradiating means, a sampling pitch SPx in the track direction of
the optical recording medium is set to satisfy:
in order to satisfy the sampling theorem. A sampling pitch SPy in
the direction perpendicular to the track direction is set to
satisfy: ##EQU3##
An embodiment of the present invention will be described with
reference to the accompanying drawings.
FIG. 2 schematically shows an optical system of a recording and
reproducing apparatus of an optical recording medium according to
the present invention, and FIG. 3 is a block diagram of the main
part of the recording and reproducing apparatus of the optical
recording medium. The optical system of the recording and
reproducing apparatus of the optical recording medium will be
described. A light beam emitted by a laser diode array 12 is
directed as incident light to a polarization beam splitter through
a collimator lens 14. The incident light is focused by a .lambda./4
plate 18 and an objective lens 20 and irradiates the optical
recording medium having a plurality of tracks, e.g., a desired
track 22 of an optical disk.
Light reflected by the track 22 is directed to the polarization
beam splitter 16 through the objective lens 20 and the .lambda./4
plate 18. The reflected light is separated from the incident light
by the polarization beam splitter 16 and is sent to a photodiode 24
as a photodetector.
In the recording and reproducing apparatus, an output from a laser
diode driver 26 is supplied to a switch circuit 28. The switch
circuit 28 performs switching in response to a timing pulse
supplied from a timing circuit 30 and outputs a driver output to
the laser diode array 12. The light beam emitted from the laser
diode array 12 is output to the photodiode 24 through the path of
FIG. 2 described above.
An output from the photodiode 24 is amplified by an amplifier 34,
passes a sample and hold circuit 36, and is output to an A/D
converter 38. A digital output from the A/D converter 38 is stored
in a frame memory 40. Data read out from the frame memory 40 is
output from a two-dimensional decoder 46 through a two-dimensional
low-pass filter (LPF) 42 and a peak detector 44.
The operation of this embodiment will be described.
FIG. 4 schematically shows the track 22 of the optical recording
medium described above, i.e., the optical disk. Guide tracks 48 are
formed on two sides of the track 22 in the track direction, and a
plurality of recording pits 50 are formed at a predetermined
interval. The recording pits 50 are recorded as different data
depending on their positions with respect to the track 22. These
recording pits 50 are read when the laser diode array 12 scans them
in the track direction and a direction perpendicular to the track
direction in a two-dimensional manner.
The laser diode array 12 is driven by the laser diode driver 26.
For example, laser diodes A, B, C, . . . , G in FIG. 3 of the laser
diode array 12 are switched in response to predetermined timing
pulses supplied from the timing circuit 30. The laser diode array
12 sequentially turned on by the timing pulses obliquely irradiates
and scans the desired track 22 through the collimator lens 14, the
polarization beam splitter 16, the .lambda./4 plate 18, and the
objective lens 20. In other words, e.g., spots 52A, 52B, 52C, 52D,
52E, 52F, and 52G in FIG. 4 obliquely irradiate the track 22 and
the guide tracks 48.
The arrangement of the laser diode array 12 corresponding to the
respective spots 52A to 52G will be described.
The arrangement of the laser diode array 12 must be set as follows
in accordance with the known sampling theorem in order to reproduce
the light reflected by a recording pit 50 on the track 22 by the
two-dimensional LPF 42. More specifically, the pitch Py in the
direction perpendicular to the track direction is set to 1/2 or
less that of the light beam spot system. A cycle for re-exciting a
single laser diode (e.g., the laser diode A of the laser diode
array 12 of FIG. 3) must be set shorter than a time required for a
detection head of an optical system 10 to move 1/2 the minimum
repetition cycle W of the recording pit 50.
More specifically, the arrangement pitch (Px) of the laser diode
array 12 in the track direction must be set to satisfy the
following relation: ##EQU4## where W is the minimum repetition
cycle of the data recording pits in the track direction, n is the
number of arrays, and l is a natural number, by considering the
shift amount of the head of the optical system 10 in the track
direction such that the detection data can be stored in a
corresponding area in the frame memory 40.
The arrangement of the laser diode array 12 for obliquely radiating
the light beam to the track and the guide tracks 48 is thus
determined. Note that if the medium moves in a direction opposite
to its moving direction shown in FIG. 4, Px must satisfy:
##EQU5##
FIGS. 5A and 5B show a state in which the laser diode array 12
appropriately irradiates the track 22 and the guide tracks 48 and a
state in which it does not, respectively, i.e., on- and off-track
states. More specifically, the discrimination between on- and
off-track states can be made depending on which one of the spots
52A to 52G corresponding to the laser diode array 12 a guide track
48 crosses. If it is discriminated to be the off-track state,
correction is performed by a servo system (not shown) to obtain the
on-track state.
Data of a recording pit 50 scanned by the spots 52A to 52G is
received by the photodiode 24 through the objective lens 20, the
.lambda./4 plate 18, and the polarization beam splitter 16. The
photodiode 24 receives light sequentially reflected by the spots
52A to 52G corresponding to the respective laser diodes A to G of
the laser diode array 12. When optical data is converted into an
electrical signal by the photodiode 24, it is then amplified by the
amplifier 34 as a reproduced signal. Then, the reproduced signal
passes the sample and hold circuit 36, is converted into a digital
signal by the A/D converter 38, and is stored in the frame memory
40.
FIG. 6 shows an example of the memory content of the frame memory
24 when the spots are sequentially radiated to perform sampling, as
shown in FIG. 4. The frame memory 24 is, e.g., a 7.times.14 byte
memory. Referring to FIG. 7, circles indicated by solid lines show
the arrangement positions of the laser diodes for forming the spots
52A to 52G as shown in FIG. 4. Circles indicated by broken lines
show the positions of the spots obtained by sequentially turning on
the laser diodes. The spot positions represent shift amounts upon
movement of the medium.
More specifically, the circles indicated by the broken lines
correspond to the spots 52A to 52G of FIG. 4. The centers of the
spots G1 and A7 are located on a line in the same track width
direction. In this example, n=7 and l=2. When the spots 52A to 52G
read data as shown in FIG. 4, the data are written at Al, Cl, . . .
, and Gl (hatched portions) of the frame memory 40 shown in FIG. 6.
Subsequently, when the laser diode array 12 is moved, the data are
written at al, bl, cl, . . . , and gl.
The reproduced signal read out from the frame memory 40 in the
longitudinal direction of the memory is processed by the
two-dimensional LPF 42 and the peak detector 44 to detect the
two-dimensional peak position of the recording pit 50. Then, the
reproduced signal is decoded by the two-dimensional decoder 46 and
is derived as recorded data through an error correction circuit and
the like (not shown).
The two-dimensional LPF 42 comprises a two-dimensional convolution
filter and also serves as a waveform equalizer.
In this manner, the recording pits arranged in a two-dimensional
manner are scanned in the two directions, i.e., the track direction
and the direction perpendicular to it, and multi-value recording is
performed within a range where a predetermined C/N (error rate) can
be ensured. As a result, the recording density can be largely
improved, and recording and reproduction can be correctly
performed.
FIGS. 8 through 10 show the second embodiment of the present
invention. FIG. 8 schematically shows an optical system of a
recording and reproducing apparatus of an optical recording medium
according to the second embodiment of the present invention. FIG. 9
is a block diagram of the main part of the recording and
reproducing apparatus of the optical recording medium. FIG. 10
shows an image-forming state on the surface of a photodiode array
of FIG. 8. In this embodiment, the same portions as in the first
embodiment described above are denoted by the same reference
numerals and a detailed description thereof will be omitted to
avoid redundancy.
The optical system of the recording and reproducing apparatus of
the optical recording medium shown in FIG. 8 will be described. A
laser diode array 54 so positioned as to obliquely scan a track 22
emits a plurality of light beams at once. The light beams as the
incident light irradiate the desired track 22 of the optical disk
through a collimator lens 14, a polarization beam splitter 16, a
.lambda./4 plate 18, and an objective lens 20. Light reflected by
the track 22 is directed to the polarization beam splitter 16
through the objective lens 20 and the .lambda./4 plate 18, is
separated from the incident light, and forms an image on a detector
array 58 through an image-forming lens 56.
The detector array 58 comprises, e.g., a linear array CCD 66 having
a photodiode array 60, a gate array 62, and a shift register 64 as
a transfer element, as indicated in an optical system 10.sub.1 of
FIG. 9.
FIG. 10 shows an image-forming state on the photodiode array 60 of
the linear array CCD 66. Images 60A, 60B, 60C, 60D, 60E, 60F, and
60G are formed between a plurality of dead zones 600.
When CCD transfer is performed by the linear array CCD 66, the
light beams can be read as time signals. As the laser diodes are
turned on at once, no switching circuit 28 or a timing circuit 30
is required. A signal read from the linear array CCD 66 is
converted into a digital signal by an A/D converter 38 in the same
manner as in the first embodiment described above, and is stored in
a frame memory 40. A reproduced signal read out from the frame
memory 40 is sent to a two-dimensional LPF 42 and a peak detector
44 so that the two-dimensional peak position of a recording pit 50
is detected. Then, the reproduced signal is decoded by a
two-dimensional decoder 46.
The laser diode array 54 can be of a type that converts a beam of a
single laser diode into a rectangular beam by a cylindrical
lens.
In the above embodiment of the present invention, tracking servo is
performed. A case in which tracking servo is not performed will be
described.
When, e.g., a disk medium is used as the optical recording medium,
eccentricity of about several tens of tracks usually occurs in the
recording tracks with respect to the center of rotation. For this
reason, the number of spots 52A to 52G shown in FIG. 4 is increased
to cover the eccentricity amount of several tens of tracks. The
number of elements of the photodiode array 58 is also increased
accordingly.
The memory capacity of the frame memory 40 of FIG. 9 is increased
to cope with the increased number of elements. Then, the position
data on the recording pits 50 and the guide tracks 48 of several
tens of tracks is stored in the frame memory 40. As a result,
tracking can be performed by reading out the position data on the
recording pits 50 while electronically tracking the guide tracks 48
in the frame memory 40 without performing mechanical tracking. As
electronic tracking is used, mechanical tracking becomes
unnecessary, and the size and weight of the detection head can be
decreased.
FIGS. 11 through 14 show the third embodiment of the present
invention. FIG. 11 schematically shows an optical system of a
recording and reproducing apparatus of an optical recording medium
according to the third embodiment of the present invention. FIG. 12
is a block diagram of the main part of the recording and
reproducing apparatus of the optical recording medium. FIG. 13
shows a scanning state on a track. FIG. 14A is a waveform chart of
a photodiode output obtained by scanning of FIG. 13, and FIG. 14B
is a waveform chart of an actuator pulse for moving a laser diode.
In this embodiment, the same portions as in the first and second
embodiments described above are denoted by the same reference
numerals and a detailed description thereof will be omitted to
avoid redundancy.
Referring to FIG. 11, a laser diode 68 is movable by an actuator 70
in the direction of an arrow J. A light beam as incident light
emitted by the laser diode 68 irradiates a desired track 22 of an
optical disk through a collimator lens 14, a polarization beam
splitter 16, a .lambda./4 plate 18, and an objective lens 20. Light
reflected by the track 22 is directed to the polarization beam
splitter 16 through the objective lens 20 and the .lambda./4 plate
18, separated from the incident light, and received by a photodiode
24.
Referring to FIG. 12, the signal received by the photodiode 24 is
output to a guide track detector 72 and a pit portion detector 74.
The guide track detector 72 detects a guide track 48 from a
difference in intensity between light reflected by the track 22 and
light reflected by a guide track 48. The pit portion detector 74
detects a recording pit 50 from a difference in intensity between
light reflected by the track 22 and light reflected by the
recording pit 50. Signals detected by the guide track and pit
portion detectors 72 and 74 are sent to a counter 76 and used
respectively as start and stop signals for the counter 76. The
counter 76 performs counting based on a predetermined clock
supplied from a clock generator 78. Namely, the counter 76 counts
data of the distance between the guide track 48 and the pit 50.
When the laser diode 68 is moved by the actuator 70 in the
direction of an arrow J in FIG. 11, a corresponding spot 52 moves
over the track 22 and the guide tracks 48 as indicated by a long
and short dashed line and a broken line in FIG. 13. When a pulse is
output from the actuator 70 as shown in, e.g., FIG. 14B, the output
of the photodiode 24 becomes as shown in FIG. 14A along with the
movement of the spot 52.
In other words, the outputs of the photodiode 24 at times t1, t2,
t3, and t4 are the outputs from the guide tracks 48, and the
outputs at times t1', t2', and t3' are the outputs representing the
recording pits 50. Note that the position of a recording pit 50 is
expressed by a distance between it and a guide track 48 on one
side. In this embodiment, only the data obtained by movement in the
broken line in FIG. 13 is used for this.
Therefore, when a distance between the points t1 and t1' and a
distance between the points t3 and t3' are measured, the position
of a recording pit 50 can be obtained. Namely, when the distance
between the points t1 and t1' and the distance between the points
t3 and t3' are counted by the counter 76, the position of the
recording pit 50, i.e., data can be obtained.
The actuator pulse corresponding to the maximum leftward movement
in FIG. 14B is deviated from a photodiode output time point (tx to
t3). Tracking servo (not shown) is performed by adjusting tracking
by using this.
In order to move the spot 52 over the track 22 and the guide tracks
48 as shown in FIG. 13, the optical system is modified such that
the output light from the laser diode 68 is reflected by a mirror
or the like, in place of moving the laser diode 58, and the mirror
is pivoted.
FIGS. 15A and 15B, and FIG. 16 show the fourth embodiment of the
present invention. An optical system is of a type used in a
conventional optical disk apparatus. As shown in FIG. 15A, a pickup
82 including a laser diode is moved in the direction of an arrow L
over an optical disk 80 as an optical recording medium rotating in
the direction of an arrow K. The pickup 82 including a laser diode
moving in the direction of the arrow L is moved without tracking
for a distance corresponding to the eccentricity of the optical
disk 80.
Then, a spot corresponding to this laser diode sequentially moves
over the track 22 and the guide tracks 48 at a pitch 1/2 the spot
diameter, as shown in FIG. 15B. Light reflected by the track 22 or
a guide track 48 is received by a photodiode 84 shown in FIG. 16
and converted into an electrical signal.
The signal is digitized by an A/D converter 38 and stored in a
frame memory 40. Then, the pickup 82 is moved as shown in FIG. 15A,
and data of several tracks is stored in the frame memory 40 by the
spot moving at the 1/2 pitch. This enables detection of the track
position on the frame memory 40. As a result, recorded data can be
detected while performing electronic tracking by the frame memory
40 and an electronic tracking circuit 86.
In FIG. 17, a plurality of laser diode arrays 88.sub.1, 88.sub.2,
88.sub.3, 88.sub.4, and 88.sub.5 each identical to the laser diode
array 12 shown in FIG. 1 are arranged. The laser diode arrays
88.sub.1, 88.sub.2, 88.sub.3, 88.sub.4, and 88.sub.5 are arranged
at such positions (heights) that, when they are turned on, they
form corresponding images of the track 22 as focused points
92.sub.1, 92.sub.2, 92.sub.3, 92.sub.4, and 92.sub.5 shown in FIG.
18.
More specifically, the focused points 92.sub.1, 92.sub.2, 92.sub.3,
92.sub.4, and 92.sub.5 of light beams 94.sub.1, 94.sub.2, 94.sub.3,
94.sub.4, and 94.sub.5 emitted by the laser diode arrays 88.sub.1,
88.sub.2, 88.sub.3, 88.sub.4, and 88.sub.5 fall within a range
indicated by an arrow M in FIG. 18. The range M is the allowable
surface swing length of the disk having the track 22.
Photodiode arrays 90.sub.1, 90.sub.2, 90.sub.3, 90.sub.4, and
90.sub.5 are set to correspond to the laser diode arrays 88.sub.1,
88.sub.2, 88.sub.3, 88.sub.4, and 88.sub.5. When the optical system
is configurated in this manner, focusing can be electronically
performed by the frame memory 40 in the same manner as in the
embodiments described above. As a result, the mechanical portion
for performing tracking and focusing can be omitted, and the size
and weight of the detection head can be reduced.
In the above embodiments, multi-value recording and reproduction by
way of two-dimensional modulation of a track direction and a track
width direction perpendicular to it are described.
Three-dimensional modulation of multi-value recording and
reproduction is possible if modulation recording is also performed
in a pit depth direction (direction perpendicular to both the track
direction and the track width direction), and recording density is
greatly increased.
In the pit recording method with modulation in the two- or
three-dimensional direction described above, regarding the track
width direction, laser diodes corresponding in number to the steps
of multi-value recording are arranged. The light beams from the
laser diodes are focused on a medium track to form a pit, thereby
performing recording. Regarding the pit depth direction, recording
can also be performed by, e.g., changing the power of the laser
diodes.
Furthermore, it is apparent that the present invention can use a
material using an Al reflecting layer (CDROM), a Te-based material,
a colorant-based material, a phase change material (write type), a
photomagnetic material, a phase change material (reversible type),
or the like as the recording material.
Additional advantages and modifications will readily occur to those
skilled in the art. Therefore, the invention in its broader aspects
is not limited to the specific details, and representative devices,
shown and described herein. Accordingly, various modifications may
be made without departing from the spirit or scope of the general
inventive concept as defined by the appended claims and their
equivalents.
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